I think around chapter 4-6 you can build this. Not sure. I'm only on ch. 11 so far.
Heavy frame or elite.
Upper tool: Telsa Tip: Diffraction torus
Lower tool: Plasma Tip: default
Put a couple of damage and/or fire rate for the upper tool. Reload speed for lower tool.
You need to build "Diffraction torus" if don't have asap.
The gun fire slow, tiny delay after pressing trigger, 1 shot 1 kill electric bolt gun, on normal every thing except bossess and unkillable necro will die 1 hit. If you hit enemy, it will arc to other enemies the closer the more damage. 1 of the level with a giant drill, I came back to this area with 4 soldiers huddle close in a circle, 1 shot all 4 dead.
This is high damage yet ammo efficient weapon. But you need good aim, if you miss you won't do any damage, no aoe damage if miss. That's where the lower force gun comes in, later you will have mass critters swarm, when anything get too close, blow them away with force gun, then zap them.
Use statis attachment if you have, disable the unkillable ubermorph instantly with 1 shot. Statis mod goes well with the freeze gun, pneumatic torch + precision tip, freeze necro instantly. Later in the game, replace the forcegun with freeze gun or flying saw blade gun.